124 



It is distinguished from all the other species by the great length 

 of the intestine, which is from six to nine times the length of the 

 body, and is spir.illy coiled aOout the air bladder. The gill-rakers 

 are numerous, about twenty in number to each gill, but are very 

 short, scarcely projecting beyond the anterior margin of the arch. 

 They are evidently almost totally inefficient as a straining apparatus. 



Of the great number of specimens available for dissection, only 

 nme were studied, since the contents of the intes'iues were found 

 so uniform in character that it was not deemed worth while to mul- 

 tiply instances. These were from both extremes and nlso fr^im the 

 center of the State, but were all taken in July. August, and Seo'em- 

 ber. The intestine was invariably filled from end to end with a 

 black and slimy matter, which, when (examined under tie micro- 

 scope, was found to consist almoi^t wholly of fine mud, ^Yhen the 

 intestine was emptied and the contents stirred up in alcohol and re- 

 peatedly decanted so as to separate the coarser fragments, the organic 

 matter was easily distinguished. It made on an average only about 

 one fourth of the contents of the intestine, the remainder consisting 

 of the finest particles of sand and clay. Not far from one fifth of 

 the whole amount was of vegetable origin, consisting chiefly of fila- 

 mentous Algse, mingled with a few diatoms, but comprising occa- 

 sionally minute fragments of other kinds of vegetation also. The 

 onlv animal objects noted were occasiontil Chironomus larva:- and- 

 Ditiiugia. Sometimes the intestine was wholly filled with almost 

 pure mud, in which no organic structures whatever could be de- 

 tected. Date and locality seemed to make no material difference in 

 the food of this fish, which should evidently be classed as limoph- 

 agous. The ratios of animal to vegetable food were scarcely dif- 

 ferent from what one would expect to find in the intestine of a fish 

 which had the habit of swallowing mud rich in organic matter, the 

 greater ratios of vegetation being apparently due to the fact that 

 plants are more abundant in the water than animals. 



PlMEPHALES PROMELAS, Raf. BlACK HeaD, 



This species is generally <listributed throughout Central and North- 

 ern Illinois, but is not very abundant. We have taken it only in 

 rivers and larger creeks, but have not found it south of Jersey 

 county. 



The alimentary canal is two to three times the length of the 

 body, and the gill rakers are fifteen in number and somewhat more 

 prominent than usual, those on the posterior part of the first arch 

 being about one third the length of the corresponding filaments. 



Only four specimens were studied, one from the Pecatonica River 

 at Freeport, and three from Otter Creek in Jersey county. With 

 this fish as with the preceding, about three fourths of the contents 

 of the Hitestine consisted of mud, the reiU'dnder being almost wholly 

 insects. These were partly terrestrial species, occurring accidentally 

 in the water, and partly aquatic larva? of Diptera. The vegetable 

 food of these specimens amounted only to about one per cent., 

 chiefly various unicellular Algas. 



